An MAC (media access control) layer protocol is designed to guarantee radio resources, such as a slot, a frequency channel, and a spreading code, etc., to a specific transmitter in a network. And for an ad hoc network, such guarantee is provided by handshake or negotiation due to the lack of central management.
Carrier sensing multiple access (CSMA) is the most popular in the MAC layer protocol. Each potential transmitter node must sense the state of a channel before actually transmitting a packet to a network. Collision may happen when the sensing fails to reflect the actual state of the channel, which is referred to as a hidden terminal problem. For a large-scale network where a large number of nodes attempt to transmit packets at the same time, the problem will become very serious. This will result in degradation of quality of service, thereby being unable to satisfy application demands.
Time division multiple access (TDMA) provides an alternative policy for the MAC layer protocol, in which exclusive time slots are reserved for transmission, so as to guarantee higher quality of service. In IEEE (Institute of Electrical and Electronics Engineers) 802.15.4 specification, a portion of a super frame, which is referred to as a collision free period (CFP), is divided for TDMA transmission. And a minimum disposable unit in such period is referred to as a guaranteed time slot (GTS).
However, the IEEE 802.15.4 specification only provides a basic GTS scheduling mechanism for the network in a star topology, which cannot support slot assignment in other sophisticated type of network, especially in the large-scale network and in ad hoc mode.
It should be noted that the above description of the background art is merely provided for clear and complete explanation of the present invention and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background art of the present invention.